(1) Field of the Invention
The invention relates to a fluid for the drilling, workover or completion of a subterranean well and to an additive and method of inhibiting the swelling of shale with such additive in such fluid.
(2) Description of the Prior Art
Applicant is aware of the following prior art patents:
______________________________________ U.S. Pat. No. Patentee ______________________________________ 2,909,858 Cannon 2,191,312 Cannon 2,956,948 Sperry 2,881,211 Sperry 2,785,125 Salathiel 3,849,317 Walker ______________________________________
The Cannon '858 and '312 patents generally disclose the use of various polyhydroxy compounds which includes certain carbohydrates, such as sucrose, which are simultaneously added with an alkaline material, such as caustic soda, in aqueous drilling fluids for purposes of inhibiting shale swelling.
While it is questionable that a "browning reaction" as hereinafter defined, occurs in the in-situ reaction of these patents, any such reaction could be undesirable in that it is performed in an uncontrolled environment. Additionally, a browning reaction which is catalyzed by acid and enzymatic initiation are not taught or suggested in such prior art.
Sperry '948 and '211 prior art patents disclose compositions prepared by acid "charring" of mono- and polysaccharides, such as glucose and sucrose, within the drilling fluids by treating the saccharides with strong mineral acids at elevated temperatures. The charred saccharides may further react with alkali metal hydroxides to form a salt for purposes of providing a water loss or emulsification agent for drilling fluids. Because of "charring" as opposed to providing a browning reaction product, the chemical compositions of the products of the Sperry '948 patent differ significantly from that of the present invention.
The Salatheil '125 patent discloses a heat-alkali treated mono-, di- or poly saccharide for use in drilling fluids which additionally contain starch for controlling water loss of the fluids.
The Walker '317 patent discloses a use of a particular mixed polysaccharide product in an alkaline drilling fluid for controlling gel strength and yield point.